Help me out someone - what should the resolution or file si…

for highest res without any waste, its about 510px wide, and whatever height you need. (72dpi)
run it through tinypng.com before posting

Thanks, I can do that in Photoshop

Thanks for asking Heather. I have wondered that too.

72dpi, about 510px wide

72dpi is a print format, just "510px wide" should work.

Baemail has a built in compressor (I'm sure Twetch does too) - but the settings are extreme on Baemail so you'll save some pennies if you copy and paste your image into Baemail Editor, & save locally

Once saved locally, use that version to upload to Twetch. Let's see what the difference is.